Laser Machining Systems and Methods with Vision Correction and/or Tracking

ABSTRACT

Vision correction and tracking systems may be used in laser machining systems and methods to improve the accuracy of the machining. The laser machining systems and methods may be used to scribe one or more lines in large flat workpieces such as solar panels. In particular, laser machining systems and methods may be used to scribe lines in thin film photovoltaic (PV) solar panels with accuracy, high speed and reduced cost. The vision correction and/or tracking systems may be used to provide scribe line alignment and uniformity based on detected parameters of the scribe lines and/or changes in the workpiece.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/439,262 filed Feb. 22, 2017, which is a divisional of U.S. patentapplication Ser. No. 14/251,926 filed Apr. 14, 2014, now U.S. Pat. No.9,604,313, which is a continuation of U.S. patent application Ser. No.12/576,508 filed Oct. 9, 2009, now U.S. Pat. No. 8,723,074, which claimsthe benefit of U.S. Provisional Patent Application Ser. No. 61/104,435,filed Oct. 10, 2008, which is fully incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to machining and more particularly, tolaser machining systems and methods with vision correction and/ortracking.

BACKGROUND INFORMATION

Laser machining systems and methods are commonly used to machine varioustypes of materials and structures. Such laser machining systems andmethods may provide a number of advantages including lower manufacturingcosts, increased throughput and production yield, and improved quality.In the area of solar panels, for example, the advantages of lasermachining could significantly enhance the efficiency and viability ofsolar energy technology.

In the manufacture of thin film photovoltaic (PV) solar panels, lasermachining techniques may be used to scribe the various thin film layersin a panel to form electrically connected cells. In one type of PV solarpanel, three layers are deposited to form the panel and lines arescribed after each new deposition. The area on the panel including theselines is considered a wasted area that does not contribute to solarenergy conversion. Thus, the lines should be straight and alignedaccurately to minimize this wasted area and to provide the bestefficiency. High scribing speeds and increased throughput are alsodesirable. Providing accurate high speed scribing of thin film PV solarpanels (and other similar structures) presents a number of uniquechallenges.

Large area workpieces, such as solar panels, may have variations inthickness and/or surface flatness and may have coating non-uniformitiesover the relatively large area, which may adversely affect machining ofthe workpiece. In particular, variations in the flatness of theworkpiece may result in variations in the process distance from a beamdelivery system, which causes changes in focus or demagnification of thelaser on the workpiece. Variations in surface flatness and thickness andcoating non-uniformities over relatively large processing distances mayresult in undesirable scribe variations such as variations in width,depth, fluence, heat-affected-zones and penetration, which can adverselyaffect the precision of the scribes. The relatively large scribingdistance also increases the chances of errors in the scribe position andorientation on a large area workpiece.

Another challenge with laser machining of PV solar panels is the abilityto maintain accuracy with the long working distance from the lasersource to the workpiece. Angular pointing instability may result fromthe long working distance and longer beam delivery path. When the laserbeam must travel longer distances to the workpiece and far-fieldscribing techniques are used, for example, the position of the laserspot focused on the workpiece can vary due to laser pointing variations,resulting in inaccuracies in line straightness and alignment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better understood byreading the following detailed description, taken together with thedrawings wherein:

FIG. 1 is a top perspective view of a laser machining system, consistentwith an embodiment.

FIG. 2 is a partially cross-sectional perspective view of the lasermachining system shown in FIG. 2 taken along an X axis.

FIG. 3 is a partially cross-sectional perspective view of the lasermachining system shown in FIG. 2 taken along a Z axis.

FIGS. 4A and 4B are front and back perspective views of a lasermachining system, consistent with another embodiment.

FIGS. 5A-5F are side schematic views illustrating the formation of linesin different layers of a thin film photovoltaic solar panel, consistentwith an embodiment.

FIG. 6 is a schematic perspective view of a laser machining systemincluding a moving optical head including a beam delivery system andsensors and cameras for use in tracking and/or vision inspection.

FIG. 7 is a diagrammatic view of a line tracking system for use in alaser machining system, consistent with an embodiment.

FIG. 8 is diagrammatic view of a workpiece tracking system for use in alaser machining system, consistent with an embodiment.

FIG. 9 is a schematic cross-sectional view of a workpiece with sensorbeams reflecting from a process plane of the workpiece.

FIG. 10 is diagrammatic view of a workpiece tracking system for use in alaser machining system, consistent with another embodiment.

FIG. 11 is a diagrammatic view of a workpiece alignment system that usesvision inspection, consistent with an embodiment.

FIG. 12 is a perspective view of a panel including multiple sets ofscribe lines formed thereon, consistent with embodiments of the lasermachining system and method.

FIG. 13 is a schematic view of a long working distance beam detectionsystem, consistent with an embodiment.

DETAILED DESCRIPTION

Vision correction and tracking systems, consistent with embodimentsdescribed herein, may be used in laser machining systems and methods toimprove the accuracy of the machining. The laser machining systems andmethods may be used to scribe one or more lines in large flat workpiecessuch as solar panels. In particular, laser machining systems and methodsmay be used to scribe lines in thin film photovoltaic (PV) solar panelswith accuracy, high speed and reduced cost. The vision correction and/ortracking systems may be used to provide scribe line alignment anduniformity based on detected parameters of the scribe lines and/orchanges in the workpiece. Various embodiments of such vision correctionand tracking systems and methods are described in greater detail below.

As used herein, “machining” refers to any act of using laser energy toalter a workpiece and “scribing” refers to the act of machining a lineon a workpiece by moving the laser and/or the workpiece linearly.Machining may include, without limitation, laser ablation scribing wherethe laser energy causes the material of the workpiece to ablate, laserrecrystallization scribing where the laser energy causes the material ofthe workpiece to melt and recrystallize, and laser stealth scribingwhere the laser energy focused internally in the workpiece causes theworkpiece to crack internally. As used herein, “flat” means havinglittle curvature but not necessarily planar. As used herein, terms suchas “substantially,” “about,” and “approximately” mean within acceptabletolerances. Various components of the laser machining systems describedherein may also be used in systems for machining workpieces having othershapes.

Referring to FIGS. 1-3, one embodiment of a laser machining system 100is shown and described, which may include a multiple beamlet laser beamdelivery system. The laser machining system 100 may include a base 102,such as a granite base, which is supported by a passive vibrationisolation system 104. The base 102 may support and provide stability forvarious components of the laser machining system 100, such as a parthandling system, optical heads, motion stages, and motion controlsystems, as described in greater detail below. The passive vibrationisolation system 104 may include four passive isolators at each cornerof the base 102 to isolate the laser machining system 100 fromvibrations that may travel along the floor. In the illustratedembodiment, the isolators are positioned between the base 102 and aframe 105.

The laser machining system 100 may include a part handling system 110for supporting a part or workpiece 101 and one or more laser scanningstages 120 supporting one or more optical heads (not shown) that directone or more laser beams at the workpiece 101. The part handling system110 may include an infeed section 110 a and an outfeed section 110 b onopposite sides of a process section 111. The part handling system 110provides a workpiece support surface 112 for supporting the workpiece101 and includes a motion control system for controlling motion of theworkpiece along a workpiece axis (e.g., Y axis), for example, to indexthe workpiece 101 through the process section 111. In particular, theinfeed section 110 a may include an infeed conveyor and the outfeedsection 110 b may include an outfeed conveyor. The infeed section 110 amoves the workpiece 101 into the process section 111 and the outfeedsection 110 b moves the workpiece 101 out of the process section 111.

In one embodiment, the part handling system 110 and workpiece supportsurface 112 may be capable of handling and supporting large panels(e.g., 1 m or greater across), such as the type used in thin film solarpanels. One embodiment of the part handling system 110 may include oneor more vacuum pucks or grippers 114 to hold the workpiece 101 (e.g.,large glass panels of a solar panel) and positioning stage(s) to movethe grippers 114. One or more of the vacuum grippers 114 may be mountedon an air bearing carriage 115 and may be independently controlled by anair bearing system to allow rotational control of the workpiece 101 forprecision alignment. A stationary vacuum puck 116 may also hold theworkpiece 101 in position during scribing in the process section 111.

An air bearing conveyor 118 may also be used to support the workpiece101 and provide high speed indexing of the workpiece 101 duringprocessing. A push-push air bearing (not shown) may also be used tosupport the workpiece 101 and prevent warping of the workpiece duringprocessing. In a push-push air bearing, an upper air gantry (not shown)may be positioned over a lower air bearing conveyor, such as conveyor118, such that air pushes the workpiece from both above and below.

In the process section 111, the laser scanning stage(s) 120 may becoupled to a laser scanning stage motion control system for moving thelaser scanning stage(s) 120 linearly along one or more scanning axes(e.g., X axis). The scanning stage 120 (and optical head) may bepositioned below the workpiece support surface 112 (and thus under theworkpiece 101) such that the optical head directs the beam(s) upwardlyat the workpiece 101 while the scanning stage 120 moves linearly alongthe scanning axis. The scanning stage 120 and motion control system mayinclude a high speed precision air bearing system, for example, capableof speeds up to about 2.5 m/sec or greater. A force cancellationtechnique or mechanism may be used to cancel or minimize reaction forcescaused by the movement of the scanning stage(s) 120 and optical head(s).Examples of force cancellation techniques and mechanisms that may beused are described in greater detail in U.S. patent application Ser. No.______ (Docket No. JPSA009) entitled LASER MACHINING SYSTEMS AND METHODSWITH MOVING LASER SCANNING STAGE(S) PROVIDING FORCE CANCELLATION, whichis filed concurrently herewith and fully incorporated herein byreference.

The laser machining system 100 also includes one or more laser sources106 that generate one or more raw laser beams and a beam delivery systemthat modifies and routes laser beam(s) to the workpiece 101. The laserwavelength may be selected based on the layer and type of material to bescribed and may include, for example, wavelengths of 1064 nm, 352 nm,355 nm, or 266 nm. The laser source(s) 106 may be located below the base102 and may be mounted on a fast access service module to minimize downtime during service intervals. The beam delivery system may modify thebeam by controlling the shape, size, uniformity and/or strength of thebeam that is routed to the workpiece 101.

The beam delivery system may include a stationary segment 108 located onthe frame 105 and/or base 102 and a movable segment located on or in themoveable optical head (not shown) on the laser scanning stage(s) 120.The stationary segment 108 of the beam delivery system may include, forexample, a series of lenses, mirrors and/or reflectors, used to directthe laser beam(s) from the laser source 106 into the movable segment ofthe beam delivery system. The mirrors or reflectors in the stationarysegment 108 of the beam delivery system may be fast steering mirrorsthat are capable of changing the direction of the beam(s) directed intothe optical heads, which may be used for beam tracking and/or forlocking the laser to improve pointing stability.

The stationary segment 108 of the beam delivery system may also includea beam expander for expanding the beam and a power meter for measuring apower of the beam. The beam expander can change both the shape and thesize of the beam and may include an arrangement of spherical lenses thatallow for independent adjustment of both beam expansion ratio anddivergence compensation. The power meter may be retractable, forexample, using a pneumatic actuator, such that the power meter may bemoved into the path of the beam to measure power readings. A retractablebeam stop may also be moved into and out of the beam path (e.g., usingpneumatic actuator). The retractable beam stop may include a mirror thatredirects the beam into a water cooled beam dump to prevent the beamfrom passing into the optical head.

As will be described in greater detail below, the moveable segment ofthe beam delivery system receives a laser beam, modifies the laser beam,and directs one or more modified laser beams to the workpiece. In oneembodiment, the beam delivery system splits a beam into multiplebeamlets to scribe multiple lines simultaneously to get a higherthroughput and uses homogenizers and/or imaging optics to make the beamless sensitive to angular pointing instability and to improve accuracy.

The laser machining system may also include a debris control system 130for collecting and removing debris generated by machining the workpiece101. In particular, the debris control system 130 may remove debrisgenerated from scribing toxic materials, such as GaAs, and othermaterials used in thin film solar panels. The debris control system 130may include a movable debris collection module or head 132 mounted on adebris control motion stage 134 above the workpiece support surface forlinear movement with the laser scanning stage 120 and optical head. Thedebris control motion stage 134 may be controlled by a motion controlsystem and slaved to the motion of the scanning stage 120. Inparticular, the debris control motion stage 134 may be an air bearinglinear motor driven stage.

The laser machining system 100 may further include air filtrationsystems and outgassing systems to filter and recycle air within theenclosure. An enclosure (not shown) may be located around the lasermachining system 100 and air filtration systems (not shown) may belocated on the enclosure. The air filtration systems filter the air toremove harmful gases and direct the filtered air back into theprocessing area within the enclosure. Examples of debris control andextraction systems and methods that may be used are described in greaterdetail in U.S. patent application Ser. No. ______ (Docket No. JPSA013)entitled LASER MACHINING SYSTEMS AND METHODS WITH DEBRIS EXTRACTION,which is filed concurrently herewith and fully incorporated herein byreference.

The laser machining system 100 may also include tracking systems and/orvision inspection systems (not shown) for precision alignment of theworkpiece prior to scribing and/or for tracking and/or inspection duringand/or after scribing. One or more sensors or inspection cameras may bemounted on the debris control motion stage 134 or another motion stagethat moves with the laser scanning stage 120. The laser machining systemmay also include computerized control systems including control softwarethat integrates the laser, motion control, digital input/output,tracking, and optional machine vision inspection. Embodiments of thetracking systems and vision inspection systems are described in greaterdetail below.

Referring to FIGS. 4A and 4B, another embodiment of a laser machiningsystem 400 is shown and described. The laser machining system 400 mayinclude a base 402 supported by passive vibration isolators 404. Thebase 402 may support and provide stability for various components of thelaser machining system 400, such as a part handling system, opticalheads, motion stages, and motion control systems.

In this embodiment, the part handling system 410 for supporting andmoving the workpiece 401 includes vacuum grippers 414 for gripping theworkpiece 401 and rollers 418 for supporting the workpiece 401. Thevacuum grippers 414 are supported on motion stages 415 capable of movingthe workpiece 401 along the indexing axis (i.e., the Y axis) to indexthe workpiece 401 through the processing section. The motion stages 415may also move the grippers 414 along the scanning axis (i.e., the Xaxis), for example, to rotate the workpiece 401.

This embodiment of the laser machining system 400 includes a laserscanning stage 420 and optical head 422 located below the workpiece 401for movement along the scanning axis. A laser source 406 mounted on thebase 402 generates a laser beam, and a stationary beam delivery system408 delivers the beam into the moving optical head 422.

This embodiment of the laser machining system 400 further includes adebris collection hood 432 mounted on the top side opposite the opticalhead 422. The debris collection hood 432 is fixed and extends across thewidth of the workpiece 401 to collect debris from the top side of theworkpiece 401 as the optical head 422 scans and machines the workpiece401 from the bottom side.

The laser machining system 400 also includes a scanning stage 434positioned above the workpiece 401, which allows the system 400 to beretrofitted for top side machining. For example, the optical head may bemounted on the scanning stage 434 and directed downward toward theworkpiece 401. In a top side machining configuration, a moving debriscollection hood may be mounted on the top side for movement with theoptical head such that the debris is extracted as the workpiece ismachined. FIGS. 4A and 4B show the system 400 configured for bottom sidemachining and thus the top side scanning stage 434 is fixed.

The laser machining system 100 may be used to scribe lines in largepanels such as solar panels. Referring to FIGS. 5A-5F, one method ofscribing lines in a thin film photovoltaic (PV) solar panel is describedin greater detail. A first (P1) layer of conductive material 510 may bedeposited on a substrate 502, such as glass or polyethyleneterephthalate (PET) (FIG. 5A). The first layer 510 of conductivematerial may include a transparent conductive oxide including, but notlimited to, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide(SnO) or zinc oxide (ZnO). The first layer 510 may then be scribed bydirecting one or more laser beams 500 through the substrate 502 to thefirst layer 510 to ablate a portion of the first layer 510 and form oneor more scribe P1 scribe lines 512 (FIG. 5B). The scribe lines 512 maybe spaced, for example, about 5-10 mm apart. The laser beam(s) 500 mayhave a wavelength (e.g., 1064 nm) and energy density sufficient toablate the P1 layer 510 without damaging the substrate 502.

A second (P2) layer 520 of an active semiconductor material may then bedeposited on the first layer 510 and within the P1 scribe lines 512formed in the first layer 510 (FIG. 5C). The semiconductor material ofthe second layer 520 may include, without limitation, amorphous silicon(aSi), cadmium telluride (CdTe), copper indium gallium diselenide(CIGS), or copper indium diselenide (CIS). The second layer 520 may thenbe scribed by directing one or more laser beams 500 through thesubstrate 502 and the first layer 510 to the second layer 520 to ablatea portion of the second layer 520 and form P2 scribe lines 522 (FIG.5D). The laser beam(s) 500 may have a wavelength (e.g., 532 nm) andenergy density sufficient to ablate the P2 layer 520 without damagingthe substrate 502 and the P1 layer 510.

A third (P3) layer 530 of a metal may then be deposited on the secondlayer 520 and in the P2 scribe lines 522 formed in the second layer 520(FIG. 5E). The conductive material of the third layer 530 may include ametal including, but not limited to, aluminum (Al), molybdenum, Mo,silver (Ag), or chromium (Cr). The second and third layers 520, 530 maythen be scribed by directing one or more laser beams 500 through thesubstrate 502 to the second layer 520 and third layer 530 to ablate aportion of the second and third layers 520, 530 and form P3 scribe lines532 (FIG. 5F). The laser beam(s) 500 may have a wavelength (e.g., 532nm) and energy density sufficient to ablate the P2 and P3 layers 520,530 without damaging the substrate 502 and the P1 layer 510.

The area with the lines 512, 522, 532 scribed in the P1-P3 layers 510,520, 530 does not contribute toward solar energy conversion and is oftenreferred to as a wasted or dead area. The lines 512, 522, 532 should bescribed and aligned accurately to minimize this dead area and providethe best efficiency of the solar panel. Embodiments of the lasermachining system and method described herein are capable of forming thelaser beams 500, directing laser beams 500 up through the substrate, andmoving or scanning the beams 500 across the substrate to form the scribelines 512, 522, 532 accurately. Embodiments of the laser machiningsystem and method described herein may also be used to scribe the lines512, 522, 532 from the top or film side by moving or scanning beamsdirected at the layers 510, 520, 530. In particular, embodiments of thevision correction and/or tracking systems described herein are capableof adjusting the beams 500 to align the scribes lines 512, 522, 532 andto provide consistent scribing width and depth.

Referring to FIG. 6, vision correction and/or workpiece tracking may beused in a laser machining system 600 that includes a moving optical head610 forming multiple scribe lines on a workpiece 601. The moving opticalhead 610 may include a beam delivery system 612 that splits a laser beam606 from a laser source 602 into multiple beamlets 616 a-616 d andimages the beamlets 616 a-616 d onto a workpiece 601. A stationary beamdelivery system (not shown) may deliver the laser beam 606 from thelaser source 602 to the moving optical head 600.

The optical head 610 is moved linearly (e.g., in the direction of arrow10) such that the beamlets 616 a-616 d form substantially parallelscribe lines 603 a-603 d along the workpiece 601 as the optical headmoves. The optical head 600 may be mounted, for example, on a laserscanning stage that moves in both directions along a scanning axis(e.g., the X axis), as described above. The laser beam 606 from thelaser source 602 is directed into the optical head 610 substantiallyparallel to the linear axis of motion (i.e., the scanning axis) and themultiple beamlets 616 a-616 d are directed out of the optical head 600substantially orthogonal to the scanning axis.

The moving optical head 610 may also be mounted on a manual or motorizedstage for adjustment across the scanning axis (e.g., along the Y axis).As such, a scanning axis of the optical head 610 may be adjusted ineither direction along the Y axis.

The beam delivery system 612 may include various components for routingthe laser beam 606 and/or beamlets 616 a-616 d and for controlling theshape, size, uniformity, and strength of the beam 606 and/or beamlets616 a-616 d. The components (not shown) of the beam delivery system 612may include, but are not limited to, a beam splitter for splitting thebeam 606 into the beamlets 616 a-616 d, a mask for shaping the beam 606or beamlets 616 a-616 d, a homogenizer for homogenizing the beam 606 orbeamlets 616 a-616 d, reflectors for routing and/or adjusting opticalpath lengths of the beamlets 616 a-616 d, and imaging optics for imagingthe mask shape on a process plane of the workpiece 601. As used herein,the “process plane” refers to a plane on or in the workpiece where thelaser is directed to machine the workpiece, for example, by causingablation. Examples of the beam delivery systems that may be used aredescribed in greater detail in U.S. patent application Ser. No. ______(Docket No. JPSA012) entitled LASER MACHINING SYSTEMS AND METHODS WITHMULTIPLE BEAMLET LASER BEAM DELIVERY SYSTEM, which is filed concurrentlyherewith and fully incorporated herein by reference.

The laser beam may be a noncoherent beam having a top hat profile. Asused herein, “noncoherent” refers to a laser beam that does not haveperfect spatial or temporal coherence. Noncoherent laser beams do notproduce undesirable interference effects when passing through fly eyehomogenizers or other types of beam homogenizers. According to oneembodiment, the laser source 602 may include a multimode laser thatprovides a multimode laser beam that has a M² factor greater than 1 andmore particularly between 5 and 25. According to another embodiment, thelaser source 602 may include a singe mode laser (M²=1) that generates acoherent Gaussian laser beam and a coherence scrambler (not shown) toprovide the noncoherent beam with a top hat profile. Examples ofcoherence scramblers include noncoherent optical fiber scramblers, lightpipes, or optical kaleidoscopes. Noncoherent beams have higher power forthe same input power and may be more desirable for homogenizing,overfilling a mask and/or shaping into the desired imaging profile. Theuse of a noncoherent beam is facilitated by using a near field imagingtechnique in which image accuracy is not as dependent upon laserpointing (e.g., as compared to a far field technique in which the focalpoint of the beam is used and pointing shows up at the focus of thelens).

The laser source 602 may be chosen to provide selective material removalwithout being destructive to other layers or the substrate. As discussedabove, for example, the second (P2) layer should be selectively removedwithout damaging the first (P1) layer. In particular, the wavelength ofthe laser may vary depending upon the characteristics of the materialbeing removed. The pulse width may also vary depending upon the type andthickness of material and may generally range between about 5 ps (orless) and about 500 ns (or less) and the frequency may be in the rangeof about 30 kHz to 1 MHz. The use of ultra fast and subpicosecondprovide a precise material removal rate and allow depth control, forexample, when scribing the P2 and P3 lasers described above.

One or more of the components of the beam delivery system 612 may becapable of adjusting the beam 606 and/or beamlets 616 a-616 d, therebyadjusting the scribe lines 603 a-603 d formed on the workpiece 601. Thepositioning of the beamlets 616 a-616 d may be adjusted, for example, bymoving a mask, beam splitter or other components in the direction ofarrow 12 orthogonal to the scanning axis (i.e., along the Y axis). Thefocus of the beamlets 616 a-616 d may be adjusted, for example, bymoving the imaging optics in the direction of arrow 14 along the beamletaxes (i.e., the Z axis). The fluence of the beamlets 616 a-616 d may beadjusted, for example, by adjusting the attenuation of the beam 606 orbeamlets 616 a-616 d.

The laser machining system 600 may also include a part handling system620 including one or more workpiece supports (e.g., vacuum chucks orgrippers) and workpiece positioning stage(s) for moving the workpiecesupports. The workpiece positioning stage moves the workpiece supportsalong an indexing axis (i.e., the Y axis) to index the workpiece,allowing another set of scribe lines to be formed. The workpiecepositioning stage and workpiece supports may also be capable of movingthe workpiece along the scanning axis (i.e., the X axis) or rotating theworkpiece (i.e., about the Z axis and in the X-Y plane).

The laser machining system 600 may further include one or moremonitoring devices for monitoring parameters or characteristics of theworkpiece 601, the scribe lines 603 a-603 d, and/or the beamlets 616a-616 d. Data from these monitoring devices may be used to adjustprocessing parameters and/or may be logged as the data is collected. Themonitoring devices may include one or more sensors 630, 640 mounted formovement with the moving optical head 610 to sense a workpiece position,a scribe line position, or other conditions as the optical head 610 isscanning. A scribe position sensor 630 may be used to sense a positionof a scribe line on the workpiece 601 to provide scribe line tracking,as described in greater detail below. A height sensor 640 may be used tosense a process plane or surfaces of the workpiece 601 for determining arelative height of the workpiece or a thickness of the workpiece 601.The sensors 630, 640 may be mounted to the optical head 610 or to ascanning stage that moves the optical head 610.

The monitoring devices may also include one or more cameras 650, 652,654 for viewing the workpiece 601, the processing area, and/or thescribe lines 603 a-603 d. At least one scanning camera 650 may bemounted for movement with the optical head 610 for viewing theprocessing area and/or scribe lines as the optical head 610 is scanning.The scanning camera 650 may be mounted to the optical head 610 or to ascanning stage that moves the optical head 610. One or more alignmentcameras 652, 654 may be positioned for viewing ends of the scribe linesto determine a width, position, and/or angle of rotation of the scribelines. The alignment cameras 652, 654 may be mounted stationary at eachside of the laser machining system 600 to view the respective ends ofone or more of the scribe lines. Although the alignment cameras 652, 654are shown beneath the workpiece 601, the alignment cameras 652, 654 mayalso be located above the workpiece 601.

One or more monitoring devices 660 may also be mounted for movement withthe optical head 610 on an opposite side of the workpiece 601. Themonitoring device(s) 660 may include, for example, a camera for viewingthe processing area and/or scribe lines as they are formed on theworkpiece 601, a sensor for sensing a scribe line or workpiece surfaceor process plane, a spectroscopic sensor for sensing optical emissionspectra created by the scribe, and/or a beamlet power meter formonitoring power of the beamlets. Monitoring devices may also beprovided in other locations within the laser machining system.

A laser machining system, consistent with embodiments described herein,may further include one or more tracking systems that track workpieceand/or scribing conditions and adjust scribing parameters in responsethereto. When scribing lines on large panels, such as solar panels, theprocess parameters, positional offsets, and other elements, may bevaried to provide uniform, aligned scribe lines. Uniform scribe linesmay have substantially uniform depth, width, heat-affected-zones (HAZ)and penetration into non-scribed layers. To provide uniformity in thescribe lines, the scribing may need to be adjusted to compensate forcertain non-uniformities in the workpiece such as the lack of surfaceflatness, glass thickness and/or coating non-uniformities. Withoutcompensation, variations in the distance from a workpiece to a focusingor imaging lens, for example, may cause undesirable scribe variations(e.g., in width and/or fluence).

Referring to FIG. 7, an embodiment of a line tracking system 700 for alaser machining system is described in greater detail. The line trackingsystem 700 may be used with laser machining systems and optical headssuch as those described above. According to one embodiment, the linetracking system 700 may align scribe lines by sensing a position of apreviously scribed line 703 on a workpiece 701 and adjusting thescribing of a current scribe line on the workpiece 701 in response tosensed changes in the position of the previous scribe line 703. Theposition of the current scribe line may be adjusted in real time totrack the position of the previous scribe line such that the currentline has a substantially constant relative separation from the previousline 703. In a thin film PV solar panel, for example, a P2 scribe linemay be aligned with a P1 scribe line and a P3 scribe line may be alignedwith a P2 or P1 scribe line. The alignment may be relative to theleading edge, center, or trailing edge of the previous scribe line.

The line tracking system 700 may include a position sensor 730 to sensethe position of the previous scribe line 703 in a directionsubstantially perpendicular to the scribe line (e.g., a position alongthe Y axis). The position sensor 730 may include a reflective sensorwith an emitter and receiver mounted on a scanning stage 711 or on anoptical head on the scanning stage 711. Alternatively, the positionsensor 730 may use a through beam arrangement with a receiver mounted onthe scanning stage 711 and an emitter on the opposite side of theworkpiece 701, or vice versa.

The position of the current scribe line may be adjusted by moving thebeamlet optically and/or by positioning the workpiece 701 in a directionsubstantially perpendicular to the scribe line. One embodiment of thebeam delivery system 712 may include a mask 714 to shape multiplebeamlets 716 a-716 d and imaging optics 718, such as a lens array, toimage the beamlets on a process plane of the workpiece 701 using a nearfield imaging technique. The mask 714 includes apertures for receivingeach of the beamlets 716 a-716 d, which back illuminate and overfill themask 714. To move the scribe optically, a mask positioning stage 732 maybe used to move the mask 714 in the direction substantiallyperpendicular to the scribe line(s), thereby adjusting the position ofthe beamlets 716 a-716 d along the indexing axis (i.e., the Y axis) onthe workpiece 701. A lateral shift adjustment of the scribe lines 703may be performed more accurately by moving the mask 714 due to thedemagnification ratio of the imaged beamlets (i.e., a shift of the mask714 results in a proportionately smaller shift of the image on theworkpiece 701), thereby increasing scribe line alignment accuracy.

The beamlets may also be moved optically using other techniques, forexample, by moving other components in the beam delivery system thatwill result in shifting the position of the beamlets or by using fastturning mirrors. For example, the image optics 718 (e.g., a focus lensarray) may be moved laterally to provide a lateral shift of the scribelines. The stages used to move the mask or other components may be PZTstages or voice coil positioning stages. The entire beam delivery system712 may also be moved along the indexing axis, for example, bypositioning the optical head on a Y axis stage.

The line tracking system 700 also includes a motion controller 734 forcontrolling the movement and positioning of the mask positioning stage732. The motion controller 734 receives the scribe position informationfrom the position sensor 730 and determines if the previous scribeposition has changed (e.g., in the Y axis) by a certain amount. If theposition has changed, the motion controller 734 causes the positioningstage 732 to move by a corresponding amount such that the relativeseparation between the lines is substantially constant. The motioncontroller 734 may receive position feedback information (e.g., from anencoder) representing a position of the mask positioning stage 732 anduses the position feedback to control positioning of the stage 732.Moving the scribe line optically may also require a corresponding changein focus, for example, by adjusting the lens array or imaging optics 718as described below.

The motion controller 734 may further be used to control movement ofother optical components or the workpiece 701 to change the position ofthe current scribe in response to changes in position of a previousscribe in a similar manner. For example, other optical componentscapable of shifting the beamlets laterally may be coupled to apositioning stage that is controlled by the motion controller 734. Oneor more positioning stages for positioning the workpiece 701 may also becontrolled by the motion controller 734. The line tracking system 700may also be incorporated with a height tracking system or workpiecethickness tracking system, as described below.

Referring to FIGS. 8-10, an embodiment of a workpiece tracking system800 for a laser machining system is described in greater detail. Theworkpiece tracking system 800 may be used with laser machining systemsand optical heads such as those described above. In general, theworkpiece tracking system 800 measures an aspect of the workpiece andadjusts a scribing parameter in response to changes in the workpiece.The workpiece tracking system 800 may measure, for example, the relativeheight of a workpiece 801 and adjust a focus of the beamlet(s) inresponse to changes in the relative height. The workpiece trackingsystem 800 may also measure a thickness of the workpiece 801 and adjusta focus and/or fluence of the beamlet(s) in response to changes in theworkpiece thickness.

The workpiece tracking system 801 may include one or more sensors 840 orother devices for measuring the relative height and/or thickness of theworkpiece 801. The sensor(s) 840 may be mounted on the scanning stage811 or on an optical head on the scanning stage 811 to measure relativeheight and/or thickness. In an embodiment, the sensor 840 may be locatedwithin the processing section at a point ahead of the scribing process.Although one sensor 840 is shown on one side of the beamlets 816,sensors may be located on both sides of the beamlets 816 such that theheight and/or thickness of the workpiece may be measured ahead of thescribing process when the scanning stage is moved in either directionalong the scanning axis (i.e., the X axis).

The sensor 840 may be a laser sensor, such as a laser interferometer orlaser triangulation sensor, capable of sensing one or more surfaces ofthe workpiece 801 and/or a process plane of the workpiece 801. As shownin FIG. 9, the relative height may be determined by sensing andmeasuring the relative height of a process plane within a workpiece. Inthis example, the workpiece 901 includes a substrate 905, such as aglass panel, and one or more coatings 907, such as the P1-P3 layers, onthe substrate 905. In this example, the process plane of the workpiece901 is the interface 909 between the substrate 905 and one of thecoatings 907 on the substrate 905. The laser beam 916 is imaged onto theinterface 909 to remove a portion of the one or more coatings 907,thereby forming a scribe line 903. Sensor beams 941, 943 emitted by oneor more sensors (not shown in FIG. 9) are reflected from the interface909 to sense changes in a relative height of the interface 909. Thesensors 840 may also be capable of sensing the surfaces and/or processplane of a workpiece from a top side.

The relative height may also be determined by sensing and measuring therelative height of the top or bottom surfaces of the workpiece using thesensor 840. The relative height of the bottom surface of the workpiece801 may also be measured using other non-contact measurement devicessuch as a sliding vacuum/air-bearing puck with a LVDT displacementsensor or using contacting measurement device that contact the bottomsurface. The contacting measurement devices may include a mechanicalfollower that contacts the near or bottom surface of the workpiece 801and a displacement measurement device such as a potentiometer, linearvariable differential transformer (LVDT), or rotary variabledifferential transformer (RVDT).

The thickness of the workpiece may be measured by using the sensor 840to sense the vertical position of both surfaces of the workpiece 801.The sensor 840 may be a laser interferometer or a laser triangulationsensor used to track the far or top surface and the near or bottomsurface of the workpiece 801 and thus measure thickness between thesurfaces. A coating or optical filter may be used to differentiatebetween the top and bottom surfaces of the workpiece 801. The sensor 840may also be a reflective sensor with an emitter and a linear arrayreceiver mounted on the moving scanning stage 811. The reflection fromeach of the surfaces records a relative maximum on the receiver arraywith the height of each surface being inferred from the locations of themaxima. The thickness may then be determined as the difference in theheights of each surface. In some embodiments, the same sensor 840 may beused to measure both the relative height and the thickness of theworkpiece 801. The range of measurement may depend on the specificationof the workpiece and the resolution and accuracy may depend on theprocessing requirements, but ranges of ±2.5 mm with sub 1.0 μmresolution may be typical.

According to an embodiment of the workpiece tracking system 800, theheight and/or thickness information may be used to change the focus ofone or more beamlets 816 imaged on a process plane of the workpiece 801.The beamlet(s) 816 are imaged onto the process plane using imagingoptics including a focusing or imaging lens 824 (or lens array formultiple beamlets). To change the focus, a lens positioning stage 842may be used to move the lens 824 relative to the workpiece 801 and alongthe axes of the beamlets (e.g., along the Z axis). The lens positionstage 842 may include a leadscrew or ballscrew positioning stage, avoice coil positioning stage, or a piezoelectric motorized stage.Changing the focus of the beamlet(s) 816 changes the width and fluenceof the beamlet(s) 816 imaged onto the process plane of the workpiece801. The focus may also be changed by moving a mask and fixed lenstogether, which may provide a more sensitive movement due to thedemagnification factor.

The workpiece tracking system 800 also includes a motion controller 844for controlling the movement and positioning of the lens positioningstage 842. The motion controller 844 receives the position informationfrom the sensor 840 or other such device and determines if the heightand/or thickness has changed by a certain amount. If the height and/orthickness have changed, the motion controller 844 causes the positioningstage 842 to move to change the focus by a corresponding amount. As therelative height increases, for example, the motion controller 844 maycause a corresponding change in the position of the lens 824 toward theworkpiece 801 to maintain a consistent focus, thereby compensating forlack of flatness of the workpiece. The corresponding change in positionof the lens 824 is not necessarily directly proportional to thevariation in height and/or thickness but may follow some function ofheight and/or thickness variation, which may be determined by testingscribes. The motion controller 844 may also receive stage positionfeedback information and use that position feedback to controlpositioning of the stage 842. The workpiece tracking system 800 may thuschange the focus in real time to image the beamlet(s) consistently onthe workpiece as the scanning stage 811 moves along the scanning axis.Other components within the beam delivery system may also be movedsimilarly instead of or together with the focusing lens 824 to track theheight and/or thickness of the workpiece 801.

Although a real time workpiece tracking system is described above, thelens 824 or other components may also be positioned based onmeasurements taken along the scanning axis in a region of the workpiecethat has not yet been processed. In one such embodiment, a plurality ofstationary sensors may be located at multiple locations along thescanning axis to record the height and/or thickness information at eachlocation along a region of the workpiece before that region is locatedin the processing area (i.e., opposite the optical head). The heightand/or thickness information measured at each location along that regionmay be used to calculate a motion profile slope (e.g., using linear orhigher order interpolation) to be followed by the motion controller 844when that measured region is subsequently indexed into the processingarea.

In another embodiment, the sensor 840 on the stage 811 or optical headmay be offset from the lens 824 such that the sensor 840 moves parallelto the process and along a region of the workpiece 801 that has not yetbeen processed. The sensor 840 records the exact curvature of theworkpiece 801 along this region and this pre-recorded motion profile maybe used by the motion controller 844 when that measured region reachesthe processing area. As shown in FIG. 10, for example, the sensor 840may record a motion profile along the scribing axis (i.e., the X axis)in a region 815 a while lenses 824 direct beamlets 816 at the workpiece801 to scribe lines along a region 815 b. When the workpiece 801 isindexed (i.e., along the Y axis) such that the region 815 a ispositioned in the processing area for scribing, the motion controller844 may use the motion profile measured for that region 815 a to movethe positioning stage 842.

Other embodiments of a workpiece tracking system may also vary otherprocessing parameters to track changes in workpiece conditions such asheight and/or thickness. Varying scan fluence as a function ofthickness, for example, may conserve energy and limit undesirableincreases in heat affected zone (HAZ) and/or undesirable penetrationinto adjacent layers of coatings. Scan fluence may be varied, forexample, using programmable attenuators or by varying laser energy. Bychanging laser parameters in response to workpiece conditions such asthickness, a laser machining system may conserve laser powerconsumption. Other optical elements or components may also be moved toadjust other processing parameters. For example, beam shaping optics maybe moved to change the size and/or shape of a beam, thereby adjustingenergy density or fluence of the beam.

According to another embodiment, a tracking system may use real timematerial spectroscopy. This type of tracking system captures opticalemission spectra created by the scribe and uses the spectra to adjustprocess parameters in real time. The optical emission spectra may becaptured using a spectroscopic sensor on the opposite surface from thescan. The material that are scribed (e.g., the P1-P3 layers in a solarpanel) have characteristic optical emission spectra. The emissionspectra of the plume generated by laser machining the layers willindicate which materials are being removed and the intensity willindicate how much is being removed. The background continuum may also beused to estimate plume temperature and pressure based on Wien's Law,which states that objects of different temperature emit spectra thatpeak at different wavelengths. Process parameters, such as fluence andfocus of the beamlets, may be adjusted in real time based on theemission spectra data.

Thus, workpiece tracking systems allow scribe variations, such as widthand fluence, to be minimized when scribing large, non-planar workpiecesor large, non-uniform coated workpieces.

Referring to FIG. 11, embodiments of a vision correction system 1100 aredescribed in greater detail. The vision correction system 1100 may beused with laser machining systems and optical heads such as thosedescribed above. According to one embodiment, the vision correctionsystem 1100 may align scribe lines by determining a position and/ororientation of a previously scribed line 1103 and adjusting a positionand/or orientation of a new scribe line based on the position and/ororientation information for the previous scribe line.

The vision correction system 1100 may include one or more alignmentcameras 1152, 1154 to view the scribe lines 1103 on the workpiece 1101.The alignment cameras 1152, 1154 may be digital progressive scancameras. The alignment cameras 1152, 1154 may be stationary and mountedat opposite sides of the laser machining system at substantially thesame position in the Y axis such that the cameras 1152, 1154 view atleast one of the scribe lines 1103 proximate respective ends of thescribe line. By viewing end portions of a scribe line, the rotationangle θ of the scribe line, the width of the scribe line, and theposition of the scribe line in the Y axis may be determined. Thesevalues may be stored in a data log, for example, in real time duringoperation of the laser scribing system.

The position and/or orientation of a new scribe line may be adjusted byadjusting a position and/or orientation of the workpiece 1101 beforescribing with an optical head 1110. A part handling system 1120 mayinclude one or more workpiece supports 1122, 1124, such as vacuumgrippers or chucks, and one or more positioning stages capable of movingthe workpiece supports 1122, 1124 in the X or Y axes. The part handlingsystem 1120 moves the workpiece in the direction of the Y axis to indexthe workpiece for sequential scribing operations and to adjust theposition at which the scribe lines are formed on the workpiece 1101 inthe Y axis. The part handling system 1120 may further rotate theworkpiece 1101 within the X-Y plane to adjust the orientation of theworkpiece 1101 and thus the scribe lines formed on the workpiece 1101.

The vision correction system 1100 may also include an image processor1155 for processing an image obtained by the cameras 1152, 1154 and amotion controller 1156 for controlling movement of the part handlingsystem 1120 by causing movement of one or more of the stages coupled tothe workpiece supports 1122, 1124. The image processor 1155 may processan image of the scribe line, for example, to determine a rotation angleand/or position in the Y axis. The motion controller 1156 may receivethe rotation angle and/or position information for the previous scribeline, and use this information to determine if the position of theworkpiece 1101 should be adjusted in the Y axis or if the rotation ofthe workpiece 1101 should be adjusted such that a subsequent new scribeline is aligned with the previous scribe line.

In one embodiment, the workpiece supports 1122, 1124 may each besupported on X-Y axis stages moveable in the X and Y axes to adjust boththe rotational angle θ and the position in the Y axis. In anotherembodiment, the workpiece supports 1122, 1124 may be coupled to apivoting support 1126 that is pivotable about a pivot point 1125 toadjust the rotational angle θ of the workpiece 1101. The pivotingsupport 1126 may be pivoted by a motor controlled by the motioncontroller 1156. The workpiece supports 1122, 1124 and pivoting support1126 may be supported on a Y axis stage to provide the Y axis indexingand positioning.

As shown in FIG. 12, multiple sets of scribe lines may be formed in oron a workpiece 1201 with sequential passes of an optical head. In oneexemplary embodiment, the alignment cameras may be used to view a scribefrom each pass as the next set of scribes is being formed. Thus, thealignment cameras view a scribe (e.g., the 4^(th) scribe) from Pass 1 asthe optical head moves to form the scribes on Pass 2 and corrections maybe made before Pass 3 based on the determined position and/ororientation of the scribe from Pass 1.

The workpiece 1201 may be indexed such that a subsequent set of scribelines is formed adjacent a previous set of scribe lines (e.g, each Passshown in FIG. 12 is formed adjacent a previous Pass). A subsequent setof scribe lines may also be formed to overlay a previous set of scribelines, for example, by indexing the workpiece 1201 or by adjusting thescanning axis of the optical head in along the indexing axis (i.e.,along the Y axis).

A shown, the scribe lines may also be inset from the edge of theworkpiece 1201 at each end of the scribe line, for example, by startingand stopping the laser when the optical head is at the desired positionat the beginning and end, respectively, of a scan. The laser may beturned on when the optical head is at the desired start position (e.g.,providing the desired inset) and then left on for a predetermined timeto produce a fixed scribe length. When processing solar panels, forexample, providing this inset mitigates electrostatic issues. Thus, thescribe line location along the scanning axis may be corrected by turningthe laser on and off and without having to adjust the workpiece 1201 inthe direction of the scanning axis.

The length of the workpiece 1201 may also be measured “on the fly”(i.e., as the workpiece 1201 is indexed), for example, using visioninspection cameras or sensors. The measured length of the workpiece 1201may be used to center the scribe lines on the workpiece 1201. Bymeasuring the length, for example, a center line 12 of the workpiece1201 may be located and the optical head may be moved to a desired startposition relative to the center line 12.

Referring to FIG. 13, a laser machining system 1300 may also include abeam position tracking system for tracking a position of a laser beamand adjusting the laser beam to assure beam pointing stability at a longworking distance. The laser machining system 1300 may include a base1302, a laser source 1306 for generating the laser beam, and an opticalhead 1310 into which the beam is directed, for example, as described inone of the embodiments above.

In one embodiment, the beam position tracking system may include a quaddetector or other position detector 1350 that is located at a longworking distance from the laser 1306 to compensate for laser beamstability issues in a long working distance system. The quad detector orother position detector 1350 may be located at a long working distancethat is at least as long as the scan distance and may be twice the scandistance or longer. For example, the laser beam emitted from the laser1306 may be split by a beamsplitter 1352 and wrapped around a perimeterof the base 1302 of the laser machining system 1300 to provide the longworking distance detection.

The quad detector or other position detector 1350 may also be locatedinside of the moving optical head 1310 to account for motion stagetravel errors and compensate for slide straightness in addition to laserbeam pointing issues. In other embodiments, the beam may also travelthrough the optical head 1310 to the detector 1350. The beam positiontracking system may also include fast steering mirrors 1354 for changingthe direction of the beam emitted from the laser source 1306 and afeedback circuit 1356 for receiving information from the positiondetector 1350 and causing the fast steering mirrors 1354 to change thedirection of the beam to maintain a desired beam position, for example,using techniques known to those skilled in the art. The fast steeringmirrors 1354 may also change a direction of the beam in response tofeedback from scribe sensors (e.g., sensor 730 in FIG. 7) to providescribe line tracking.

Accordingly, tracking and vision correction may be used during lasermachining to assure alignment of scribe lines and uniformity in thescribe lines. Such alignment and uniformity is particularly importantwhen scribing solar panels. One example of a laser machining system,consistent with embodiments described herein, is capable of a positionaccuracy of +/−2.5 μm.

Consistent with one embodiment, a laser machining system includes a parthandling system including a workpiece support surface for supporting aworkpiece to be machined and at least one laser source for generating atleast one laser beam. At least one laser scanning stage is positionedrelative to the part handling system for linear movement along ascanning axis, and a movable optical head is located on the laserscanning stage. The optical head includes a beam delivery system forreceiving the at least one laser beam, for modifying the at least onelaser beam, and for directing the modified beam at the workpiece whilemoving to machine the workpiece. The laser machining system furtherincludes a workpiece tracking system for tracking changes in theworkpiece relative to the moving optical head and for adjusting at leastone parameter of the modified beam in response to the changes in theworkpiece.

Consistent with another embodiment, a laser machining system includes apart handling system including a workpiece support surface forsupporting a workpiece to be machined and at least one laser source forgenerating at least one laser beam. At least one laser scanning stage ispositioned relative to the part handling system for linear movementalong a scanning axis, and an optical head is located on the laserscanning stage. The optical head includes a beam delivery system forreceiving the at least one laser beam, modifying the laser beam, anddirecting the modified beam at the workpiece while moving to form ascribe line on the workpiece. The laser machining system furtherincludes a scribe line tracking system for tracking a position of ascribe line on the workpiece and for adjusting a position of a currentscribe line being formed on the workpiece in response to changes in aposition of the scribe line.

Consistent with a further embodiment, a laser machining system includesa part handling system including a workpiece support surface forsupporting a workpiece to be machined and at least one laser source forgenerating at least one laser beam. At least one laser scanning stage ispositioned relative to the part handling system for linear movementalong a scanning axis, and an optical head is located on the laserscanning stage. The optical head includes a beam delivery system forreceiving the at least one laser beam, modifying the laser beam, anddirecting the modified beam at the workpiece while moving to form ascribe line on the workpiece. The laser machining system furtherincludes a vision correction system for viewing at least one scribe lineon the workpiece and for positioning a workpiece in response to at leastone parameter of the scribe line on the workpiece.

Consistent with yet another embodiment, a method is provided for lasermachining a panel using a movable optical head that moves along ascanning axis. The method includes: mounting the panel on a parthandling system; generating at least one laser beam; directing the laserbeam substantially parallel to the scanning axis and into at least oneoptical head such that the optical head modifies the beam and directs atleast one modified beam out of the optical head substantially orthogonalto the scanning axis; moving the optical head along the scanning axisand across the panel such that the at least one modified beam scans thepanel and forms a scribe line in the panel; and adjusting at least oneparameter in response to a detected change in the workpiece or a scribeline on the workpiece.

Consistent with yet another embodiment, a method is provided formachining a panel. The method includes: mounting the panel on a parthandling system and forming a plurality of sets of scribe lines alongthe panel. Forming each of the sets of scribe lines includes: indexingthe panel along an indexing axis; and moving an optical head along ascanning axes orthogonal to the indexing axis while directing aplurality of beamlets at the panel to form a set of scribe lines alongthe panel; and adjusting at least one scribing parameter in response toa detected parameter of the workpiece or a scribe line on the workpiece.

Consistent with yet a further embodiment, laser machining systemincludes a part handling system including a workpiece support surfacefor supporting a workpiece to be machined and at least one laser sourcefor generating at least one laser beam. At least one laser scanningstage is positioned relative to the part handling system for linearmovement along a scanning axis, and an optical head is located on thelaser scanning stage. The optical head includes a beam delivery systemfor receiving the beam and modifying the beam while moving. The lasermachining system further includes a beam position tracking systemcomprising a position detector for receiving a portion of the at leastone laser beam, wherein the position detector is located such that abeam path from the laser source to the position detector is at least aslong as a working distance of the laser beam from the laser source tothe workpiece.

While the principles of the invention have been described herein, it isto be understood by those skilled in the art that this description ismade only by way of example and not as a limitation as to the scope ofthe invention. Other embodiments are contemplated within the scope ofthe present invention in addition to the exemplary embodiments shown anddescribed herein. Modifications and substitutions by one of ordinaryskill in the art are considered to be within the scope of the presentinvention, which is not to be limited except by the following claims.

What is claimed is:
 1. A laser machining system comprising: a parthandling system including a workpiece support surface for supporting aworkpiece to be machined; at least one laser source for generating atleast one processing laser beam; an optical head including a beamdelivery system for receiving the at least one processing laser beam andfor directing the processing laser beam at the workpiece; and aworkpiece tracking system for tracking changes in the workpiece as theprocessing laser beam moves relative to the workpiece and for adjustingat least one parameter of the processing laser beam in response to thechanges in the workpiece, wherein the workpiece tracking system includesat least a laser interferometer sensor for measuring a processingdistance to the workpiece.
 2. The laser machining system of claim 1wherein the at least one laser interferometer sensor measures aprocessing distance to at least one surface of the workpiece, andwherein the workpiece tracking system tracks changes in the processingdistance to the surface of the workpiece.
 3. The laser machining systemof claim 1 wherein the at least one laser interferometer sensor measuresa processing distance to a process plane of the workpiece and whereinthe workpiece tracking system tracks changes in the processing distanceto the process plane of the workpiece.
 4. The laser machining system ofclaim 3 wherein the process plane of the workpiece is located within theworkpiece.
 5. The laser machining system of claim 1 wherein theworkpiece tracking system tracks changes in a height of the workpiecerelative to the optical head.
 6. The laser machining system of claim 1wherein the workpiece tracking system tracks changes in thickness of theworkpiece.
 7. The laser machining system of claim 1 further comprisingat least one laser scanning stage positioned relative to the parthandling system for linear movement along a scanning axis, wherein theoptical head is located on the laser scanning stage.
 8. The lasermachining system of claim 1 wherein the beam delivery system comprisesat least one lens for focusing the processing laser beam and a lenstranslation stage for moving the lens and adjusting the focus of theprocessing laser beam, and wherein the workpiece tracking systemincludes a motion controller configured to move the lens translationstage and the lens to adjust the focus of the processing laser beam inresponse to the changes in the workpiece.
 9. The laser machining systemof claim 1 further comprising at least one optical component configuredto adjust fluence of the processing laser beam in response to changes inthe workpiece.
 10. The laser machining system of claim 9 wherein theoptical component includes a programmable attenuator.
 11. The lasermachining system of claim 9 wherein the optical component includes beamshaping optics.
 12. The laser machining system of claim 1 wherein theworkpiece tracking system is configured to adjust a laser energy of thelaser source in response to changes in the workpiece.
 13. The lasermachining system of claim 1 wherein the at least one laserinterferometer sensor includes at least a first laser interferometersensor positioned relative to the optical head to track changes in theworkpiece ahead of the processing laser beam.
 14. The laser machiningsystem of claim 13 wherein the at least one laser interferometer sensorincludes at least a second laser interferometer sensor positionedrelative to the optical head to track changes in the workpiece on theother side of the processing laser beam.
 15. The laser machining systemof claim 1 wherein the workpiece tracking system further comprises aspectroscopic sensor for capturing optical emission spectra frommaterial being processed by the processing laser beam, and wherein theworkpiece tracking system is configured to adjust at least oneprocessing parameter based on the optical emission spectra.
 16. A methodof tracking changes in a workpiece during laser processing, the methodcomprising: mounting the workpiece on a part handling system; generatingat least one processing laser beam from a laser source; directing theprocessing laser beam through a beam delivery system to the workpiecewhile moving the processing laser beam relative to the workpiece;measuring a processing distance to the workpiece with a laser sensordirected toward the workpiece; and adjusting a laser parameter inresponse to changes in the processing distance measured by the lasersensor.
 17. The method of claim 16 wherein the laser sensor is a laserinterferometer sensor.
 18. The method of claim 16 wherein directing thelaser beam through a beam delivery system to the workpiece while movingthe laser beam relative to the workpiece includes scanning theprocessing laser beam across the workpiece.
 19. The method of claim 16wherein adjusting a laser parameter includes adjusting a focus of theprocessing laser beam at the workpiece.
 20. The method of claim 16wherein adjusting a laser parameter includes adjusting a fluence of theprocessing laser beam at the workpiece.